The cleaning of various substrates to exacting specifications has become a major consideration in the production of a wide variety of articles of manufacture. It is well known that chlorine-containing solvents are useful as cleaning agents for solid substrates, such as metals, aerospace components, medical devices, photographic and movie films, electronic and mechanical parts, molds for casting plastics, surfaces being prepared for painting, and various substrates in need of degreasing, including plastic and elastomeric surfaces. Molecular level cleaning by vapor degreasing has found a wide acceptance in the industry. In fact, molecular level cleaning by vapor degreasing is a preferred method for cleaning precision parts, such as electronics, machined metallic parts, etc., since vapor cleaning leaves virtually no residue on the parts.
While chlorine-containing solvents are technically suitable for such uses, many of them have now been banned or their use severely restricted because of environmental and/or health considerations. With the mandated elimination of the most popular chlorine-containing cleaning solvents, many manufactures have switched to other cleaning systems, such as aqueous and semi-aqueous systems. Although such systems have proved to be a viable alternative in many cleaning applications, they are not suitable for all applications. In the search to find more universal alternatives, a wide variety of new solvent cleaners were developed. While some of the new solvent cleaners are commercially successful, they still suffer from one or more deficiencies relative to the overall cost/performance of the chlorinated materials they replaced. For example, some of the newer solvents, such as some hydrofluorocarbons (HFCs) have been shown to meet environmental and toxicological requirements, but do not meet the highest performance standards.
The need in specialized applications for a non-chlorinated high-performance cleaning agent that could be used in a safe and efficient manner has led to the development of cleaning systems based on the solvent normal-propyl bromide (n-propyl bromide or nPB). The use of n-propyl bromide has met with some degree of commercial success. Its advantages include its effectiveness as a cleaning solvent, as well as its moderate cost, non-flammability, and low ozone depletion potential. Nevertheless, for some applications, n-propyl bromide is considered too aggressive because it has a tendency to swell and even dissolve certain plastics and elastomers. Attempts to tone-down its aggressiveness by blending it with at least one other solvent has generally led to expensive blends (with hydrofluoroethers) or flammable blends (with hydrocarbons). Therefore, there exists a need in the art for ways to mitigate the aggressiveness of n-propyl bromide without substantially reducing its effectiveness as a superior cleaning agent.